Possible Clues:

• M, L or K, for MLK
• Endorse first Latin novel about the start of the Interregnum
• The I of IPO
• First subscribe minimally
• Primary witness, on paper
• First piece of writing, one I found in Latin needing going over
• First home, one is met by wagging tail
• First letter one found in old language, then another one turned up
• C. S. Lewis piece?
• 'First in Latin, almost', I swaggered